Method and device for guiding a tool

ABSTRACT

Method and device for guiding a tool in a recurring application of a product moved along an X-axis, wherein the tool is mounted on the Z-carriage of a cross guide and is moved therewith along the Z-axis standing perpendicular on the X-axis, wherein the Z-carriage is mounted on the X-carriage of the cross guide, the guide of which is mounted along the X-axis in a base plane, wherein the X-carriage is driven with an X-drive, wherein the Z-carriage is driven by a Z-drive, which is held stationary in the base plane and has a traction means driven by a first servo motor provided for the drive of the Z-carriage, which is driven from the base plane on the movable Z-carriage, wherein a movement of the Z-carriage that is brought about by the movement of the X-carriage and a motive force caused thereby on the traction means, is compensated when actuating the first servo motor provided for the drive of the Z-carriage.

The present invention relates to a method and a device for guiding atool in a repetitive motion acting on an object. In particular, theinvention relates to the guidance of a transverse cutting knife fortransversely cutting a raised object that is moved in the transportdirection, in particular a soft food product, such as a stack of cheesebands lying on top of one another, wherein the transverse cutting takesplace perpendicularly to the transport direction of the object.

Devices for the processing, in particular also for the transversecutting, of highly diverse objects are known from a number of productionprocesses. Reference is made to WO 01/28865 A1 in this regard. Thetransverse cutting of moving, relatively flat cheese bands is alsoknown, in particular. In this regard, DE 10 2008 061 330 A1 discloses adevice for cutting individual pieces from a cheese band, which isinitially cut into longitudinal strips and is then fed by means of aconveyor belt to a transverse cutting device. This cuts the longitudinalstrips into individual pieces during the continuous motion, wherein thetransverse cutting knife is moved back to the initial position afterevery cut.

Whereas the transverse cutting of such a flat band can be carried out ina very easily implemented, short “chopping motion”, the transversecutting of a raised band, for example, a stack of a plurality of cheesebands lying on top of one another, requires a more complex motionsequence since the transverse cutting knife must be guided exactlyperpendicularly to the movement of the band for a relatively long timeduring the entire cutting motion. In addition, it is highly desirable tonot be limited to a single cut, but rather to have the option of cuttingthe bands in various lengths, for example.

In order to be capable of carrying out this type of complex cuttingmotions in a flexible manner, devices are used that utilize separatedrives for the movement along each axis. Drives that are separated inthis manner make a freely parameterizable and exact cutting sequencepossible. In addition, such efficient transverse cutting devices can beused to cut endless cheese bands into individual stacks having anylength, wherein no changeover times are required to change the guidanceof the cut.

Known transverse cuffing devices of the type used in this technicalfield have a knife holder, which is held on a slide guided by means of across guide. Such a cross guide is a system with two axis, comprisingtwo linear guiding systems each having one axis, whereby the cross guideenables a movement of an object in two directions usually with an offsetof 90° within a plane. In the known transverse cutting devices the slideis pneumatically driven along the transverse cutting direction (Z-axis).On the other hand, the drive along the conveyance direction (X-axis)utilizes a servomotor, i.e., an electric motor, which is held on a baseplate in a stationary manner, in which the angular position of the motorshaft as well as the speed of rotation and the acceleration can becontrolled by means of a sensor system. With this drive, the X-axis ofthe transverse cutting direction is synchronized with exact positioning,according to the “flying saw” principle, with the endless cheese bandthat is moving in the transport direction, wherein the knife cuts alongthe Z-axis in this synchronized movement.

A problem associated with the known devices, however, is that, duringthe pneumatically driven cutting in the Z-direction, there is noinformation available on the actual position of the knife and thus thereis no position feedback at all during the course of cutting. Inaddition, the increasing requirements on a greater cutting depth andspeed exceed the performance limit of these systems that can be achievedsuch that the process is reliable. Another disadvantage of the pneumaticZ-drive is the high energy loss in the end positions of the knife.

Although some of the aforementioned problems can be avoided with asecond servomotor that drives the movement in the Z-direction, thisconcept is not feasible for most applications insofar as the secondservomotor is mounted on the slide that is moved in the Z-direction andnegatively affects the motion sequence and, therefore, the energyconsumption, via its own weight. For example, the dimensions of thefirst servomotor would have to be increased accordingly.

A gantry drive, which is known from mechanical engineering, is anotherdrive that could be considered, in principle, for such a compound table.In this movement system, a geometrical axis of the compound table ismoved by means of two separate feed motors, which are driven in anangularly synchronous manner by means of converter control. A movementin the horizontal direction is generated when the two drives are movedin an angularly synchronous manner, i.e., with the same direction ofrotation and at the same speed, whereas a movement in the verticaldirection is generated when the two drives are moved in oppositedirections of rotation and at different speeds. Any trajectory andcoordinates in the movement area can be obtained by means of theinterplay between the two drive motors. Such a gantry drive is slow andhas limited dynamics, however, due primarily to its relatively largemass that must be moved. For this reason, the gantry drive has not beenused so far in the guidance of tools in repetitive production processes,but rather were used only for systems that can be adjusted individually,such as patient beds in therapy and diagnostic devices, for example.

The problem addressed by the present invention is therefore that ofcreating a method for guiding a tool, in particular a transverse cuttingknife, which acts on an object, in particular a moving product, in arepetitive motion, can be carried out with simple technical means, andpermits rapid, flexible, and precise handling of the tool with lowenergy consumption and great dynamics. Another problem addressed by theinvention is that of creating an easy-to-handle device for carrying outthe method.

These problems are solved by a method having the characterizing featuresof claim 1 and by a device according to claim 4. Advantageousembodiments of the invention are set forth in the respective dependentclaims.

According to the fundamental idea of the invention, a tool that ismounted on a Z-slide of an X-/Z-cross guide is driven by a firstservomotor, which is not mounted on the moving X-slide, but rather ismounted in the base plane in a stationary manner outside of the compoundtable. The first servomotor, which is therefore decoupled from themovement of the compound table, is equipped with a pulling means, inparticular a belt, which acts on the Z-slide and pulls this in theZ-direction and simultaneously permits the Z-slide to move along theX-axis. In order to meet these conditions, the pulling means is guidedalong the outer contour of a T by means of redirecting rollers, whereinthe X-axis forms the top bar of the T and the Z-axis forms the middlebar of the T. In this arrangement, the middle bar can be initiallydisplaced in a parallel manner along the top bar without movement of thepulling means. In such a parallel displacement, however, a point of thepulling means located on the middle bar travels along the middle bar. Asa result, a tool that is held at this point is forced to move along theZ-axis when the X-axis is displaced, provided the pulling means isfixed. A highly essential aspect of the invention is therefore that ofcompensating for this forced movement along the Z-axis when movementoccurs along the X-axis by means of the first servomotor and/or toaccount therefor, by means of calculations, in the control thereof.

For this purpose, information regarding the (change in) position alongthe X-axis is made available to the control of the first Z-servomotor.Such position information can be obtained from the control electronicsof a second servomotor provided for the X-drive and can be fed to thecontrol electronics of the first servomotor provided for the Z-drive.Such position information could also be derived from an external sensorsystem that registers the (change in) position along the X-axis.

In other words, the fundamental idea of the invention is that ofinitially using a drive system with which a movement along the X-axis isdirectly coupled to a movement along the Z-axis such that a movement inthe X-axis induces a “synchronous” compensation motion in the Z-axis.Since this compensation motion is unwanted during operation, thissuperposed motion is compensated for, for the Z-axis, by the control ofthe first servomotor. The feedback coupling even results in the effectthat a movement in the X-axis can support the movement of the Z-axisthat is necessary for the process sequence.

The invention is therefore manifested in that the X-slide is driven byan X-drive and the Z-slide is driven by a Z-drive, wherein the Z-driveis mounted in the base plane in a stationary manner and comprises apulling means, in particular a belt, which is driven by a firstservomotor. This pulling means is guided on the Z-slide from the baseplane, wherein a movement of the Z-slide that is caused by a movement ofthe X-slide and a resultant displacement of the pulling means along theZ-axis is compensated for in the control of the Z-drive.

For the compensation, it is advantageous if the movement of the X-slideis registered, in particular, on the basis of the control data for asecond servomotor driving the X-slide, and this value is taken intoaccount, for the purpose of the compensation, as an input variable inthe control of the X-drive during the action motion of the Z-slide.

A characteristic feature of the idea according to the invention is thatit can be used anywhere in which a tool held on a compound table is usedto act on an object, in a repetitive motion along a predefinabletrajectory, in the axis that is moved along the other axis of thecompound table. The invention makes it possible for the tool totemporarily dwell in the moving coordinate system of the object duringthe handling in which the action is carried out.

A typical application of the invention is the transverse cutting in theZ-direction of a product band, which is moved in a transport direction(X-direction) perpendicular to the Z-direction and is, for example,several centimeters thick, wherein said product band can be formed by alayered food product having a pasty consistency, such as processedcheese, for example.

It is particularly advantageous that, due to the biaxial drive accordingto the invention having the first servomotor, at least for the Z-drive,which is held in the base plane—and, advantageously, having a secondservomotor for the X-drive—the mass that is moved with the slide is keptlow such that motion sequences of the tool mounted on the cross guidethat are particularly rapid and simultaneously precise are madepossible. Due to the weight reduction of the moving mass and theperformance increase, it is possible to integrate additional modules,such as a diagonal cut or an interlayer cut, for example.

In all, the invention results in an increase in functional reliabilitysince the cutting sequence is completely regulated since there isconstant feedback and monitoring of the setpoint/actual position of thetool in the dynamic motion sequence. In addition, high energy efficiencyis given since energy is recovered in the end positions via theservotechnology and is not wasted as in the case of the pneumatic driveof the Z-axis. The result thereof is a longer service life and low-wearfunctioning. The servomotors also make it possible to increase theprocessing output (timing rate) as well as the cutting output.

A particularly great advantage of the invention is the flexibility ofthe tool guidance, which in the case of transverse cutting makes itpossible to cut any formats without mechanical retooling. In addition,due to its symmetrical design, the device can be operated symmetricallyin both directions of motion along the X-axis. With the same device, itis possible to switch from right-hand motion to left-hand motion.

A special embodiment of the invention is shown in FIGS. 1 to 3 and isdescribed in greater detail in the following. Therein:

FIG. 1 shows the transverse cutting knife of a device according to theinvention during operation, and

FIG. 2 shows the drive of the transverse cutting knife, and

FIG. 3 shows a schematic diagram of the drive.

FIG. 1 schematically shows a transverse cutting module of the type thatcan be used in the production process for producing a single stack 1 ofcheese slices. Such a single stack 1 is cut off of a stack 3 of cheesebands, which have been placed on top of one another, by means of atransverse cutting knife 2, wherein said cheese bands move on a conveyorbelt 4 continuously in the transport direction along the X-axis (arrowX), which is on the horizontal in this case. The transverse cutting ofthe stack 3 takes place, during the transport, along a Z-axis (arrow Z),which extends vertically in this example. The narrow transverse cuttingknife 2, which is mounted on the lower edge of a holding frame 5, actson the stack 3 in a repetitive, cutting manner along a predefined motioncurve. In this connection, the transverse cutting knife 2 is guided tothe point of the stack 3 at which the cut starts. It is then guidedalong with the transport motion of the stack 3 along the X-axis andsimultaneously executes a cut along the Z-axis. After the cut iscompleted, the transverse cutting knife 2 is raised up and out and isguided rearward to the next starting point. The motion curve for thiscutting action is predefined with respect to the product and theproduction cycle and is driven by two independent drives in the form ofservomotors 7 and 8, which are located behind a plate 6 and are fixedlymounted there.

FIG. 2 shows the back side of the plate, on which the servomotors 7 and8 are located, each of which is controlled by non-illustrated,programmable control electronics. Since information regarding themomentary rotational angle of the servomotors is available, the controlelectronics know the actual position of both servomotors and can accountfor the current position of one in the control of the other. Acompensation means is therefore implemented in the control electronicsfor controlling the two servomotors and, in the control of one of thetwo servomotors, accounts for the control parameters of the respectiveother servomotor. In this manner, it is possible, in particular, tocompensate for a motion of the transverse cutting knife 2 in theZ-direction that is caused by movement in the X-direction, in thecontrol of the Z-drive. The influence on the movement in the Z-directionby a movement in the X-direction is described with reference to FIG. 2.

As is evident from FIG. 2, the device comprises a cross guide having twoslides, namely an X-slide 10, which is guided by means of an X-guidehaving the rails 9 a, 9 b, and a Z-slide 12, which is guided by means ofa Z-guide having the rails 11 a, 11 b. The transverse cutting knife isheld on the Z-slide and the rails 11 a, 11 b for the Z-slide are mountedon the X-slide 10, as shown. In contrast, the rails 9 a, 9 b for theX-slide are mounted in a stationary manner on a base plane 13 (baseplate).

The X-drive for driving the X-slide takes place by means of the secondservomotor 7, which is mounted on the base plane 13 and drives a pullingmeans in the form of a belt 14. The X-slide is fixedly coupled to thebelt 14 and is pulled forward or backward along the X-axis by this belt,depending on the direction of rotation of the second servomotor 7. Thebelt 14 is redirected by means of a redirection roller 15, which ismounted “coaxial” with the second servomotor 7, relative to the X-axis,on the base plane 13.

The drive of the Z-slide 12 is designed similarly to that of the X-slide10 and also has a first servomotor 8, which is held in the base plane ina stationary manner, and a redirection roller 16, which is mounted“coaxial” with the first servomotor 8, relative to the X-axis, on thebase plane 13. The first servomotor 8 and the redirection roller 16therefore form two redirections that are held in the base plane. Thefirst servomotor 8 drives a pulling means in the form of a belt 17. Inthe case of the Z-drive, the belt 17 is guided in a T-shaped path, whichhas an X-leg with bottom pull 18 and top pull 24 and a Z-leg 19.

The operating method of the drive of the compound table via the belts isillustrated in FIG. 3. The movement of the X-slide 10 in the X-direction(arrow) is driven by the second servomotor 7, which acts on the X-slide10 via the belt 14. The belt 14 is fixed on the X-slide 10 at the points22. The drive of the Z-slide 12 with the first servomotor 8, which isheld in a stationary manner, utilizes the belt 17, which is guided in aT-shaped path and the top pull 24 of which branches off in a loop, whichforms the Z-leg 19, via two tension rollers 20 and 20 a held on theX-slide 10. The belt 17 is redirected via a roller 21, which is held onthe X-slide 10 at the end of the Z-leg 19. The Z-slide 12 is held on thebelt 17 at the points 23 and is moved in the Z-direction (arrow) on theX-slide via the belt 17.

As is evident from the schematic diagram according to FIG. 3, a movementof the X-slide with the belt 17 fixedly held causes the Z-slide 12 tomove, since the loop forming the Z-leg 19 is displaced and the Z-slide12 fixed at a point 23 of the belt 17 moves relative to the X-slide.According to the invention, a compensation means is now available, whichundertakes the control of the two servomotors 7 and 8 such that thismovement of the Z-slide caused by the movement of the X-slide iscompensated for by the Z-drive at least to the extent that is necessaryfor the desired motion sequence of the transverse cutting knife held onthe Z-slide 12.

As described above, the method and the device for guiding a tool in arepetitive action on an object moving along the X-axis provides in apreferred embodiment the following: A device (forming a cross-drive)comprising an X-slide 10 capable of moving solely along the X-axis, aZ-slide 12 mounted on the X-slide 10 capable of moving perpendicular tothe X-axis, and a tool 2 mounted on the Z-slide 12. The X-slide 10 isdriven with an X-drive whereby in a preferred embodiment the X-slide 10engaged with a second belt 14 engaged with a second servomotor drive 7and a second fixed pulley 15 for moving the X-slide along the X-axis.The Z-slide 12 is engaged with a first belt 17, which is engaged with afirst servomotor drive 8 and a second fixed pulley 16.

In that embodiment, at least the first servomotor drive 8 and the firstfixed pulley 16 and, when present, the second servomotor drive 7 and thesecond fixed pulley 15, are mounted at fixed locations relative to eachother. The X-slide 10 comprises a first traveling pulley 20 and a secondtraveling pulley 20 a, wherein the first traveling pulley 20 and thesecond traveling pulley 20 a are each fixedly mounted on the X-slidebelow the Z-slide 12 and redirecting the belt 14 from a horizontaldirection to a vertical direction. The X-slide 10 further comprises athird traveling pulley 21, wherein the third traveling pulley 21 isfixedly mounted on the X-slide above the Z-slide 12 and redirecting thebelt 14 from the first traveling pulley 20 to the second travelingpulley 20 a, whereby the Z-slide 12 may be engaged with the belt 14between the first traveling pulley 20 and the third traveling pulley 21for driving the Z-slide 12 perpendicular to the X-axis.

An article 3 moving along the X-axis may be provided, which moves alongthe X-axis. In a preferred embodiment, the X-slide 10 is driven alongthe X-axis by the second servomotor drive 7 via the second belt 14,while the Z-slide 12 is driven along the Z-axis with the firstservomotor drive 8 via the first belt 17. As described above, the firstservomotor drive 8 is controlled such that a movement of the Z-slide 12caused by movement of the X-slide 10 and the resultant tractive force onthe first belt 17 is compensated.

For that, advantageously the movement of the X-slide 10 is registeredand used as an input variable for controlling the second servomotordrive 8.

The device may further comprise an electronic control device forcontrolling the second servomotor drive 7 and the first servomotor drive8 for coordinating movement of the tool 2 via the second servomotordrive 7 and first servomotor drive 8.

The invention claimed is:
 1. A device for guiding a tool in a repetitiveaction on a moving product, wherein the device comprises a cross guide,wherein the tool is held on a Z-slide, the guidance of which defines theZ-axis of the cross guide, wherein the Z-slide is movably held on anX-slide, the guidance of which defines the X-axis, which isperpendicular to the Z-axis, wherein the guidance along the X-axis ismounted in a base plane, wherein an X-drive is provided to drive theX-slide, for the drive of the Z-slide, a Z-drive is held in the baseplane in a stationary manner, said Z-drive comprising a belt driven by afirst servomotor provided for the drive of the Z-slide, wherein the beltis guided in a T-shaped path, which has an X-leg and a Z-leg, whereinthe X-leg extends around two pulleys held in the base plane and forms atop pull and a bottom pull, wherein the top pull branches via a firsttension roller and a second tension roller held on the Z-slide into aloop forming the Z-leg, said loop being guided around anotherredirection roller, which is held on the X-slide at the end of theZ-section, wherein a compensation device is provided for controlling thefirst servomotor provided for the drive of the Z-slide so as tocompensate for a movement of the Z-slide caused by a movement of theX-slide.
 2. The device according to claim 1, wherein one of theredirections is a redirection roller, which is drivable by the firstservomotor provided for the drive of the Z-slide is mounted on the shaftof the first servomotor provided for driving the Z-slide.
 3. The deviceaccording to claim 1, wherein the X-drive comprises a belt, which isoperated by a second servomotor and is redirected in a loop in the baseplane.
 4. The device according to claim 1, wherein the tool is atransverse cutting knife, which is adapted for cutting-, in a repetitivecutting process, a product moving at a conveyance speed in theconveyance direction along the X-axis.
 5. The device according to claim1, wherein the compensation device is implemented in the controlelectronics for controlling the two servomotors and, in the control ofone of the two servomotors, accounts for the control parameters of therespective other servomotor.